JPH06160375A - Measuring method and device for acidity of fruit juice - Google Patents

Abstract

PURPOSE:To precisely measure acidity even in fields with ease by obtaining relation between acidity of fruit juice and pH in advance and then measuring pH of a to-be-measured fruit juice for inverse calculation. CONSTITUTION:A buffer liquid, prepared in advance, is mixed with the fruit juice of known concentration, for generating calibration curve, and the value is converted into data such as table form to be stored in a computer unit 5, and then through inverse calculation, acidity is calculated and displayed from the pH of fruit juice actually measured. In other words, a pH electrode 1 and a temperature electrode 2 are set in a measurement cell 3, and their outputs are converted into digital quantity with an AD converter 4 provided with an amplification circuit, and then inputted in the computer unit 5. Here, inverse calculation is done, and acidity is directly displayed on a display equipment 6. Therefore fruit juice acidity is easily measured with precision by anyone anywhere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the acidity of fruit juice, which is mainly used for quality control of fruits for agriculture. More specifically, the pH of the fruit juice is measured and determined in advance. The present invention relates to a method for measuring acidity based on the relationship between pH and acidity of juice, and a device for directly reading the measured acidity.

[0002]

2. Description of the Related Art The acidity of fruit juice has hitherto been measured by titration analysis using a sodium hydroxide solution. However, this method is a manual analysis method using a general chemical analysis instrument, and its operation is complicated and requires skill. Therefore, on-site measurement is difficult.

In addition, as a simple measuring method, a method has been devised in which the acidity is indirectly determined by diluting fruit juice with water and measuring its electrical conductivity. However, this method cannot avoid the influence of electrolytes other than the acid contained in the fruit juice, and since the dilution ratio is as high as several tens of times, it is easily affected by the measurement error. It could only be used for simple preliminary tests.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a measuring method and a measuring apparatus for fruit acidity, which can measure fruit acidity even in the field such as outdoors, and can be accurately measured by a simple operation requiring no learning. To do.

[0005]

According to the present invention, in order to achieve the above-mentioned object, the relationship between the acidity and the pH of the fruit juice is preliminarily determined by using a buffer solution prepared so as to match the predetermined acidity of the fruit juice. There is provided a method for measuring the acidity of fruit juice, characterized in that the pH of the fruit juice to be measured is measured and the acidity of the fruit juice is calculated from the above relationship. Furthermore, according to the present invention, means for measuring the pH of the mixed solution of the buffer and the fruit juice prepared so as to be compatible with the predetermined acidity of the fruit juice, and the previously determined pH and acidity of the fruit juice mixed solution. There is also provided a fruit juice acidity measuring device comprising means for converting the pH value of the fruit juice measured based on the relationship into acidity and displaying the acidity.

[0006]

The action and mode of the present invention is as follows. The measurement of the fruit acidity according to the present invention is carried out by mixing a buffer solution prepared in advance according to the fruit acidity (acidity or the amount of acid) to be measured at a fixed ratio, and mixing the mixture. By measuring the pH of the liquid, it is automatically converted into the acidity and displayed based on the relationship between the pH and the acidity obtained in advance.

The structure and operation of the present invention will be described below with reference to the drawings. FIG. 1 is a plot of pH changes obtained by adding a certain amount of acid component contained in fruit juice to sodium hydroxide and a buffer solution having the same specified amount. The point indicated by EP is the end point in the titration method, but in the case of the buffer solution, a relatively gentle curve is drawn before and after the buffer solution, and this curve can be adjusted by adjusting the composition. Follow this graph in reverse, p
If we try to estimate the amount of acid added (hence, the acidity of the solution) by knowing H, the end point (E
P) Accurate estimation is possible only in a narrow range in the vicinity. That is, in the range of the acid amount other than the vicinity of the end point, the curve is in a nearly horizontal state, and even a slight difference in pH due to a measurement error causes a large change in the acid amount, which makes it impossible to perform accurate measurement. On the other hand, in the case of using the buffer solution, it is possible to estimate in a wider range, and further, the formulation of the buffer solution can be arbitrarily designed according to the required accuracy and measurement range.

Focusing on one kind of fruit juice, a mixture of the fruit juice and the prepared buffer solution at a constant ratio exhibits a constant pH depending on the amount of acid contained therein. That is, when the pH of a specific fruit juice is measured by changing the amount of the acid contained in the juice, a curve (calibration curve) showing the relationship between the pH and the amount of the acid as shown in FIG. 1 is obtained. Therefore, the amount of acid in the fruit juice can be known by measuring the pH of the fruit juice whose acidity is to be measured. Specifically, a pre-prepared buffer solution and fruit juice of known concentration are mixed to create a calibration curve,
This value is stored in a computer as data such as a table, and the acidity is calculated from the pH of the fruit juice actually measured by inverse calculation and displayed. Alternatively, the corresponding scale of acidity is also written on the display scale of the pH meter based on the calibration curve created in advance, so that the acidity can be directly read on the pH meter along with the pH of the fruit juice actually measured in an analog manner. Appropriate acidity indicating means can be adopted.

In this way, a means for formulating a buffer solution for various juices so as to obtain a calibration curve having an appropriate slope and displaying the juice acidity corresponding to the measured pH based on the calibration curve is provided. It may be installed in the measuring device.
Since the range of acidity contained depending on the type of fruit falls within a fixed value, if a buffer solution is designed for each type of fruit and supplied to the customer, it is not necessary for the customer to make this design.

[0010]

[Examples] Hereinafter, examples in which the acidity meter according to the present invention is actually applied to mandarin orange juice will be shown and described in more detail, but it goes without saying that the present invention is not limited to the following examples. FIG. 2 is a block diagram of the measuring unit of the acidity meter according to the present invention. A pH electrode 1 and a temperature electrode 2 are installed in the measuring cell 3. This output is converted into a digital quantity by the AD converter 4 with an amplifier circuit and is a computer unit (CPU).
Input to 5. Here, the inverse operation described above is performed, and the acidity is directly displayed on the display 6.

In this example, NaOH, Na ₂ HPO ₄ , Na ₂ B ₄ O are used so that the acidity of the juice contained in the fruit juice is converted into the amount of citric acid to measure the juice acidity of 1 ± 0.2%. _A buffer was formulated from ₇ and NaHCO ₃ . This solution 10c
FIG. 3 shows a calibration curve prepared by mixing the m ³ and 0.5 cm ³ of juice having a known acidity in the measuring cell 3 and making the mixture in the measuring section. It is a calibration curve having an appropriate slope, and it was shown that the acidity can be easily obtained from pH. In the actual measurement, the buffer solution 10c
It suffices to mix m ³ and 0.5 cm ³ of juice of unknown concentration in the measuring cell 3 and read the numerical value output on the display 6. 10 cm ^3, for the amount of 0.5 cm ^3, are both graduated cylinder, weighing the use of the pipette suitable instrument easily and accurately perform weight was shown that procedure also simple.

[0012]

EFFECTS OF THE INVENTION According to the present invention, since anyone can easily and accurately measure the acidity of fruit juice, the accurate acidity of fruit juice, which has conventionally been forced to be picked and carried to a laboratory, etc. Measurements can be made on site such as fields. As a result, it is possible to know exactly when the fruit should be harvested, and to ship the fruit in a state of high quality and high market value. In addition, collectors and distributors can also measure at the collection site and at the store, ensuring quality and increasing the added price.

[Brief description of drawings]

FIG. 1 pH when acid components contained in fruit juice are added to sodium hydroxide and a buffer solution having the same specified amount.
It is a graph which shows the change of.

FIG. 2 is a schematic configuration diagram of a measuring unit of a fruit juice acidity measuring device according to an embodiment of the present invention.

[Fig. 3] p measured in orange juice in Examples
It is a graph which shows the relationship (calibration curve) between H and the amount of citric acid conversion of fruit juice acidity.

[Explanation of symbols]

1 pH electrode, 2 temperature electrode, 3 measuring cell, 4
AD converter with amplification circuit, 5 computer units (CPU), 6 indicators.

Claims (2)

[Claims] 1. The relationship between the acidity and the pH of the fruit juice is obtained in advance by using a buffer solution prepared so as to match the acidity of the predetermined fruit juice, and the pH of the fruit juice to be measured is measured to obtain the above relationship. A method for measuring the acidity of fruit juice, which comprises determining the acidity of the fruit juice. 2. A means for measuring the pH of a mixed solution of a buffer solution and a fruit juice prepared so as to adapt to a predetermined acidity of the fruit juice, and a relationship between the pH and the acidity of the fruit juice mixture solution obtained in advance. An apparatus for measuring the acidity of fruit juice, which comprises means for converting the measured pH value of the fruit juice into acidity based on the display.